Liquid-jetting apparatus and method of driving the same

Abstract

The liquid-jetting apparatus has a liquid-jetting head with nozzle openings through which liquid particles are jetted. The liquid-jetting head performs a flushing operation to remove the thickened liquid from the nozzle openings to recover its normal liquid-jetting ability. The flushing operation jets liquid particles having a weight of 10 ng or below successively through the nozzle openings at a jetting speed of 8 m/s or above. The liquid-jetting apparatus is capable of achieving a satisfactory flushing operation to ensure a satisfactory liquid-jetting characteristic by recovering from a thickened state in a liquid in the nozzle openings even if the liquid is un-uniformly thickened in the nozzle openings.

What is claimed is:  
     
       1. A liquid-jetting apparatus comprising: 
       a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; and  
       a recovering unit to recover from a state of thickened liquid in the nozzle openings, the recovering unit including a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, the minute liquid particle having a weight of less than 10 ng and being jetted at a jetting speed of 8 m/s or above.  
     
     
       2. The liquid-jetting apparatus according to  claim 1 , wherein the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet liquid particles through the nozzle openings; and 
       wherein the flushing unit has a driving unit to drive the pressure generating means for the flushing operation.  
     
     
       3. The liquid-jetting apparatus according to  claim 2 , wherein the pressure generating means includes piezoelectric members capable of deforming the pressure chambers to jet liquid particles through the nozzle openings, and 
       wherein the driving unit gives a driving signal to the piezoelectric member.  
     
     
       4. The liquid-jetting apparatus according to  claim 1 , wherein the flushing unit is capable of carrying out the flushing operation selectively in a first flushing mode or a second flushing mode, 
       wherein the flushing operation of the first mode jets a minute liquid particle having a weight of less than 10 ng at a jetting speed of 8 m/s or above, and  
       wherein the flushing operation of the second mode jets a minute liquid particle having a weight of 12 ng or above.  
     
     
       5. The liquid-jetting apparatus according to  claim 1 , 
       wherein the liquid-jetting head is provided with pressure chambers respectively communicating with the nozzle openings and capable of containing the liquid, and pressure generating means driven by liquid-jetting signals to vary pressure in the pressure chambers such that the liquid particles are jetted through the nozzle openings,  
       wherein the flushing unit drives the pressure generating means by a driving signal for flushing, and  
       wherein the driving signal for flushing is generated independently of the liquid-jetting signal.  
     
     
       6. The liquid-jetting apparatus according to  claim 5 , wherein a meniscus of the liquid formed in the nozzle opening is retracted greatly immediately before the minute liquid particle is jetted by the flushing unit, and the minute liquid particle is jetted through a central part of the meniscus. 
     
     
       7. A liquid-jetting apparatus comprising: 
       a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings;  
       a recovering unit to recover from a state of thickened in a liquid in the nozzle openings, the recovering unit comprising a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, the minute liquid particle having a weight of 10 ng or below and being jetted at a jetting speed of 8 m/s or above,  
       wherein the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet liquid particles through the nozzle openings,  
       wherein the flushing unit has a driving unit to drive the pressure generating means for the flushing operation,  
       wherein the pressure generating means comprises piezoelectric members capable of deforming the pressure chambers to jet liquid particles through the nozzle openings,  
       wherein the driving unit outputs a driving signal to the piezoelectric member, and  
       wherein the driving signal given by the driving unit to the piezoelectric member comprises:  
       a first voltage-raising part to apply a voltage for expanding the pressure chamber so that the pressure in the pressure chamber is reduced to the piezoelectric member,  
       a first voltage holding part to apply a voltage for maintaining the pressure chamber at a reduced pressure to the piezoelectric member,  
       a first voltage-reducing part to apply a voltage for contracting the pressure chamber to raise the pressure in the pressure chamber to a slightly reduced pressure to the piezoelectric member,  
       a second voltage holding part to apply a voltage for maintaining the pressure chamber at the slightly reduced pressure to the piezoelectric member, and  
       a second voltage-reducing part to apply a voltage for setting the pressure chamber in its original state to the piezoelectric member.  
     
     
       8. The liquid-jetting apparatus according to  claim 7 , wherein the first voltage-raising part of the driving signal has an auxiliary voltage-maintaining part to apply a voltage to the piezoelectric member such that the pressure in the pressure chamber is maintained temporarily at a slightly or moderately reduced pressure during an expansion of the pressure chamber to reduce the pressure in the pressure chamber. 
     
     
       9. A liquid-jetting apparatus comprising: 
       a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings;  
       a recovering unit to recover from a state of thickened liquid in the nozzle openings, the recovering unit comprising a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, the minute liquid particle having a weight of 10 ng or below and being jetted at a jetting speed of 8 m/s or above, the flushing unit is capable of carrying out the flushing operation selectively in a first flushing mode or a second flushing mode;  
       a head moving mechanism to move the liquid-jetting head in a scanning direction;  
       a capping mechanism disposed in a head-moving range in which the liquid-jetting head is able to move and capable of covering the nozzle openings;  
       a timer for measuring a time elapsed after the nozzle openings have been covered with the capping mechanism; and  
       a mode control unit to selectively determine the mode of the flushing operation based on the time measured by the timer,  
       wherein the flushing operation of the first mode jets a minute liquid particle having a weight of 10 ng or below at a jetting speed of 8 m/s or above, and  
       wherein the flushing operation of the second mode jets a minute liquid particle having a weight of 12 ng or above.  
     
     
       10. The liquid-jetting apparatus according to  claim 9 , wherein the flushing unit carries out the flushing operation in the first flushing mode only when the time measured by the timer is in a range of a predetermined first time and a predetermined second time, and carries out the flushing operation in the second flushing mode when the time measured by the timer is outside the range of the first time and the second time. 
     
     
       11. The liquid-jetting apparatus according to  claim 10 , wherein the first time is two minutes, and the second time is five minutes. 
     
     
       12. The liquid-jetting apparatus according to  claim 9 , wherein the flushing unit operates in the first flushing mode in an initial stage of the flushing operation, and starts operating in the second flushing mode a predetermined time after a start of the flushing operation. 
     
     
       13. The liquid-jetting apparatus according to  claim 9 , wherein the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet the liquid particles through the nozzle openings; 
       the flushing unit has a driving unit to drive the pressure generating means;  
       the pressure generating means comprises piezoelectric members capable of deforming the pressure chambers to jet the liquid particles through the nozzle openings;  
       the driving unit outputs a first driving signal to the piezoelectric member for the flushing operation in the first flushing mode, and outputs a second driving signal to the piezoelectric member for the flushing operation in the second flushing mode; and  
       the first driving signal and the second driving signal are made by selectively using parts of a common driving signal.  
     
     
       14. The liquid-jetting apparatus according to  claim 13 , wherein the first driving signal comprises: 
       a first voltage-raising part to apply a voltage to the piezoelectric member such that the pressure chamber is expanded and the pressure in the pressure chamber is reduced to a reduced pressure,  
       a first voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the reduced pressure,  
       a first voltage-reducing part to apply a voltage to the piezoelectric member such that the pressure chamber is contracted and the pressure in the pressure chamber is raised to a slightly reduced pressure,  
       a second voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the slightly reduced pressure, and  
       a second voltage-reducing part to apply a voltage to the piezoelectric member such that the pressure chamber is restored to its original state; and  
       the second driving signal comprises:  
       a first voltage-raising part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is expanded and the pressure in the pressure chamber is reduced to a low pressure,  
       a first voltage holding part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is maintained at the low pressure,  
       a first voltage-reducing part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is contracted and the pressure in the pressure chamber is raised to a high pressure,  
       a second voltage-holding part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is maintained at the high pressure, and  
       a second voltage-raising part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is restored to its original state.  
     
     
       15. A liquid-jetting apparatus comprising: 
       a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; and  
       a recovering unit to recover from a thickened state in a liquid in the nozzle openings, the recovering unit including a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles,  
       wherein a meniscus of the liquid formed in the nozzle opening is retracted greatly immediately before the minute liquid particle is jetted by the flushing unit, and the minute liquid particle is jetted through a central part of the meniscus.  
     
     
       16. A liquid-jetting apparatus comprising: 
       a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings; and  
       a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a state of thickened liquid in the nozzle openings;  
       wherein the flushing control unit makes the nozzle opening jet at least two kinds of liquid particles among the plurality of kinds of liquid particles respectively having different volumes in one cycle of the flushing operation,  
       wherein the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes, and  
       wherein the liquid particle having the smallest volume is jetted first in one cycle of the flushing operation.  
     
     
       17. The liquid-jetting apparatus according to  claim 16 , wherein the liquid particle having the smallest volume is jetted at least twice in one cycle of the flushing operation, and the liquid particles having the smallest volume are jetted first and last, respectively, in one cycle of the flushing operation. 
     
     
       18. A method of driving a liquid-jetting apparatus having a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings, and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a state of thickened liquid in the nozzle openings; 
       wherein the flushing operation is executed by the flushing control unit so that at least two kinds of liquid particles among the plurality of kinds of liquid particles respectively having different volumes are jetted in one cycle of the flushing operation,  
       wherein the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes,  
       wherein the liquid particle having the smallest volume is jetted first in one cycle of the flushing operation.  
     
     
       19. The method of driving a liquid-jetting apparatus according to  claim 18 , wherein the liquid particle having the smallest volume is jetted at least twice in one cycle of the flushing operation, and the liquid particles having the smallest volume are jetted first and last, respectively, in one cycle of the flushing operation. 
     
     
       20. A liquid-jetting apparatus comprising: 
       a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings; and  
       a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a thickened state in a liquid in the nozzle openings;  
       wherein the flushing control unit is capable of selecting an optimum flushing mode among a plurality of flushing modes according to a degree of thickening of the liquid in the nozzle opening, and liquid particles among the plurality of kinds of liquid particles respectively having different volumes excluding a liquid particle having a largest volume are jetted for the flushing operation in any one of the plurality of flushing modes.  
     
     
       21. The liquid-jetting apparatus according to  claim 20 , wherein a volume of the liquid particle to be jetted for the flushing operation is about half a volume of the liquid particle having the largest volume among those of the plurality of kinds of liquid particles respectively having different volumes. 
     
     
       22. The liquid-jetting apparatus according to  claim 20 , wherein the liquid particle to be jetted for the flushing operation has a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes. 
     
     
       23. The liquid-jetting apparatus according to  claim 20 , wherein the liquid particles are jetted for the flushing operation by a jetting operation other than a jetting operation including steps of continuously expanding the pressure chamber to increase a volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously contracting the pressure chamber to reduce the volume of the pressure chamber, holding the pressure chamber in a contracted state, and continuously expanding the pressure chamber. 
     
     
       24. The liquid-jetting apparatus according to  claim 23 , wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to reduce the volume of the pressure chamber to a middle reduced level, holding the pressure chamber in a moderately contracted state, and continuously and sufficiently contracting the pressure chamber to a greatest reduced level. 
     
     
       25. The liquid-jetting apparatus according to  claim 23 , wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to a moderately contracted state, holding the pressure chamber in the moderately contracted state, continuously expanding the pressure chamber again to an expanded state, holding the pressure chamber in the expanded state, contracting the pressure chamber again to a contracted state, holding the pressure chamber in the contracted state, and continuously expanding the pressure chamber again. 
     
     
       26. A method of driving a liquid-jetting apparatus having a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings, and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a thickened state in a liquid in the nozzle openings, comprising: 
       selecting an optimum flushing mode among a plurality of flushing modes by the flushing control unit according to a degree of thickening of the liquid in the nozzle openings; and  
       executing the flushing operation so that the liquid particles are jetted through the nozzle openings using a selected flushing mode;  
       wherein the liquid particles among the plurality of kinds of liquid particles respectively having different volumes excluding a liquid particle having a largest volume are jetted for the flushing operation in any one of the plurality of flushing modes.  
     
     
       27. The method of driving a liquid-jetting apparatus according to  claim 26 , wherein a volume of the liquid particle to be jetted for the flushing operation is about half a volume of the liquid particle having the largest volume among those of the plurality of kinds of liquid particles respectively having different volumes. 
     
     
       28. The method of driving a liquid-jetting apparatus according to  claim 26 , wherein the liquid particle to be jetted for the flushing operation is a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes. 
     
     
       29. The method of driving a liquid-jetting apparatus according to  claim 26 , wherein the liquid particles are jetted for the flushing operation by a jetting operation other than a jetting operation including steps of continuously expanding the pressure chamber to increase a volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously contracting the pressure chamber to reduce the volume of the pressure chamber, holding the pressure chamber in a contracted state, and continuously expanding the pressure chamber. 
     
     
       30. The method of driving a liquid-jetting apparatus according to  claim 29 , wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to reduce the volume of the pressure chamber to a middle reduced level, holding the pressure chamber in a moderately contracted state, and continuously and sufficiently contracting the pressure chamber to a greatest reduced level. 
     
     
       31. The method of driving a liquid-jetting apparatus according to  claim 29 , wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to a moderately contracted state, holding the pressure chamber in the moderately contracted state, continuously expanding the pressure chamber again to an expanded state, holding the pressure chamber in the expanded state, contracting the pressure chamber again to a contracted state, holding the pressure chamber in the contracted state, and continuously expanding the pressure chamber again. 
     
     
       32. A liquid-jetting apparatus comprising: 
       a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers by pressure generating means to jet liquid particles through the nozzle openings, and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings;  
       a driving signal generating unit capable of selectively generating driving signals respectively having different frequencies for driving the pressure generating means;  
       a cleaning control unit capable of carrying out a cleaning operation that draws out the liquid through the nozzle openings by suction; and  
       a flushing control unit capable of carrying out a flushing operation that operates the pressure generating means such that the liquid-jetting head jets liquid particles through the nozzle openings into a non-recording region;  
       wherein, after a cleaning operation has been carried out by the cleaning control unit, the flushing control unit carries out a flushing operation by making the driving signal generating unit generate a driving signal of a frequency other than a highest frequency among those of the driving signals that can be generated by the driving signal generating unit to jet liquid particles having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes.  
     
     
       33. The liquid-jetting apparatus according to  claim 32 , wherein the driving signal for driving the pressure generating means for the flushing operation has a lowest frequency among those of the driving signals that can be generated by the driving signal generating unit. 
     
     
       34. The liquid-jetting apparatus according to  claim 32 , wherein the driving signal for driving the pressure generating means for the flushing operation is used also for driving the pressure generating means in a high-quality recording mode. 
     
     
       35. The liquid-jetting apparatus according to  claim 32 , wherein the driving signal for driving the pressure generating means for the flushing operation is used exclusively for the flushing operation. 
     
     
       36. The liquid-jetting apparatus according to  claim 32 , wherein a frequency of the driving signal for driving the pressure generating means for the flushing operation is in a range of 0.1 to 3 kHz. 
     
     
       37. The liquid-jetting apparatus according to  claim 32 , wherein the liquid particle used for the flushing operation has a weight in a range of 1 to 20 ng. 
     
     
       38. The liquid-jetting apparatus according to  claim 32 , wherein each of the nozzle openings jets liquid particles 1000 times or above for the flushing operation. 
     
     
       39. The liquid-jetting apparatus according to  claim 32  further comprising a minute-vibration control unit that applies a minute-vibration pulse by using a driving signal generated by the driving signal generating unit to the pressure generating means to vibrate a meniscus of the liquid in the nozzle opening for slight vibrations after completing the flushing operation. 
     
     
       40. The liquid-jetting apparatus according to  claim 39 , wherein, after the minute-vibration control unit has completed a minute-vibration operation, the flushing control unit makes the driving signal generating unit generate a driving signal of a frequency higher than that of the driving signal used for jetting the liquid particle having the smallest volume for flushing to jet a liquid particle having a volume larger than that of the liquid particle having the smallest volume through the nozzle opening into the non-recording region for a second flushing operation. 
     
     
       41. The liquid-jetting apparatus according to  claim 40 , wherein the second flushing operation uses a driving signal of the highest frequency among those of driving signals that can be generated by the driving signal generating unit to jet a liquid particle having a largest volume among those of the plurality of kinds of liquid particles respectively having different volumes through the nozzle opening. 
     
     
       42. The liquid-jetting apparatus according to  claim 32  further comprising a stationary-state control unit capable of holding the pressure generating means in a stationary state for a predetermined time after completing the flushing operation. 
     
     
       43. The liquid-jetting apparatus according to  claim 42 , wherein the predetermined time is one second or longer. 
     
     
       44. A method of driving a liquid-jetting apparatus having a liquid-jetting head provided with nozzle openings, pressure chambers respectively communicating with the nozzle openings and pressure generating means capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings, and capable of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings, a driving signal generating unit to generate a driving signal for driving the pressure generating means, capable of selectively generating driving signals respectively having different frequencies, comprising: 
       a cleaning step of cleaning the nozzle openings by drawing out the liquid through the nozzle openings by suction; and  
       a flushing step of, after completing the cleaning step, jetting liquid particles having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes through the nozzle openings into a non-recording region for a flushing operation by making the driving signal generating unit generate a driving signal of a frequency other than a highest frequency among those of the driving signals that can be generated by the driving signal generating unit.  
     
     
       45. The method of driving a liquid-jetting apparatus according to  claim 44 , wherein the driving signal to be used for the flushing operation has a lowest frequency among those of the driving signals that can be generated by the driving signal generating unit. 
     
     
       46. The method of driving a liquid-jetting apparatus according to  claim 44 , wherein the driving signal to be used for the flushing operation is used also for driving the pressure generating means in a high-quality recording mode. 
     
     
       47. The method of driving a liquid-jetting apparatus according to  claim 44 , wherein the driving signal for driving the pressure generating means for the flushing operation is used exclusively for the flushing operation. 
     
     
       48. The method of driving a liquid-jetting apparatus according to  claim 44 , wherein the frequency of the driving signal for driving the pressure generating means for the flushing operation is in a range of 0.1 to 3 kHz. 
     
     
       49. The method of driving a liquid-jetting apparatus according to  claim 44 , wherein the liquid particle used for the flushing operation have a weight in a range of 1 to 20 ng. 
     
     
       50. The method of driving a liquid-jetting apparatus according to  claim 44 , wherein each of the nozzle openings jets liquid particles 1000 times or above for the flushing operation. 
     
     
       51. The method of driving a liquid-jetting apparatus according to  claim 44  further comprising a minute-vibration step of applying a minute-vibration pulse by using a driving signal generated by the driving signal generating unit to the pressure generating means to vibrate a meniscus of the liquid in the nozzle opening for slight vibrations after completing the flushing operation. 
     
     
       52. The method of driving a liquid-jetting apparatus according to  claim 51  further comprising a second flushing step of, after the minute-vibration step has been completed, making the driving signal generating unit generate a driving signal of a frequency higher than that of the driving signal used for jetting the liquid particle having the smallest volume for flushing to jet a liquid particle having a volume larger than that of the liquid particle having the smallest volume through the nozzle opening into the non-recording region. 
     
     
       53. The method of driving a liquid-jetting apparatus according to  claim 52 , wherein the second flushing step uses a driving signal of the highest frequency among those of driving signals that can be generated by the driving signal generating unit to jet a liquid particle having a largest volume among those of the plurality of kinds of liquid particles respectively having different volumes through the nozzle opening. 
     
     
       54. The method of driving a liquid-jetting apparatus according to  claim 44  further comprising a stationary-state control step of holding the pressure generating means in a stationary state for a predetermined time after completing the flushing operation. 
     
     
       55. The method of driving a liquid-jetting apparatus according to  claim 54 , wherein the predetermined time is one second or longer.